Commit 58d5640e authored Jan 29, 2014 by Mark Rutland Committed by Linus Torvalds Jan 29, 2014

mm/readahead.c: fix do_readahead() for no readpage(s)



Commit 63d0f0a3 ("mm/readahead.c:do_readhead(): don't check for
->readpage") unintentionally made do_readahead return 0 for all valid
files regardless of whether readahead was supported, rather than the
expected -EINVAL.  This gets forwarded on to userspace, and results in
sys_readahead appearing to succeed in cases that don't make sense (e.g.
when called on pipes or sockets).  This issue is detected by the LTP
readahead01 testcase.

As the exact return value of force_page_cache_readahead is currently
never used, we can simplify it to return only 0 or -EINVAL (when
readpage or readpages is missing).  With that in place we can simply
forward on the return value of force_page_cache_readahead in
do_readahead.

This patch performs said change, restoring the expected semantics.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent a0132ac0

mm/readahead.c

+5 −10

Original line number	Diff line number	Diff line
		@@ -211,8 +211,6 @@ out:
		int force_page_cache_readahead(struct address_space mapping, struct file filp,
		pgoff_t offset, unsigned long nr_to_read)
		{
		int ret = 0;

		if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
		return -EINVAL;

		@@ -226,15 +224,13 @@ int force_page_cache_readahead(struct address_space mapping, struct file filp,
		this_chunk = nr_to_read;
		err = __do_page_cache_readahead(mapping, filp,
		offset, this_chunk, 0);
		if (err < 0) {
		ret = err;
		break;
		}
		ret += err;
		if (err < 0)
		return err;

		offset += this_chunk;
		nr_to_read -= this_chunk;
		}
		return ret;
		return 0;
		}

		/*
		@@ -576,8 +572,7 @@ do_readahead(struct address_space mapping, struct file filp,
		if (!mapping \|\| !mapping->a_ops)
		return -EINVAL;

		force_page_cache_readahead(mapping, filp, index, nr);
		return 0;
		return force_page_cache_readahead(mapping, filp, index, nr);
		}

		SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)

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